In recent years, mobile electronic appliances, such as a portable terminal, a digital camera, and a notebook, have increasingly been used. Such a mobile electronic appliance needs to have waterproof function because it is for portable use and thereby there is a risk of falling into water. That is, an acoustic hole for emitting sound is formed on a portion where a speaker, a microphone, etc. is installed, and water or dust permeates into the electronic appliance through the acoustic hole.
Accordingly, the acoustic hole is provided with a waterproof sound-transmitting sheet for passing through sound and blocking water or dust. Such a waterproof sound-transmitting sheet should be manufactured considering both waterproof performance and sound transmission efficiency.
Regarding the waterproof sound-transmitting sheet, Korean Patent Publication No. 10-2010-0041839 (Apr. 22, 2010) discloses a configuration that is composed of a porous polytetrafluoroethylene film. However, there is a problem in that the conventional waterproof sound-transmitting film is composed of only a porous polytetrafluoroethylene film, such that the micropores of the porous film gradually become larger due to externally-applied impact or sound pressure as the use period becomes long, thus reducing waterproof performance.
In order to solve the problem, a waterproof sound-transmitting sheet composed of a waterproof layer and a support layer has been conventionally developed. In this time, since waterproof performance at a water pressure of about 1 atm (BAR, about 10 m) has been required conventionally, the waterproof sound-transmitting sheet of a structure stacking the waterproof layer composed of a porous material for waterproof, and a protective layer configured to be moved by sound pressure for sound-transmission has been developed.
Meanwhile, waterproof performance at a water pressure of about 5 atm (BAR, about 50 m) has been recently required while consumer interest in waterproof performance rapidly increases.
However, there is a problem in that the conventional waterproof sound-transmitting sheet has the waterproof layer composed of a porous material, such that when a water pressure of about 5 atm is applied thereto, the hole of the waterproof layer becomes large gradually, or the waterproof layer is broken due to the collision between the waterproof layer and the protective layer, thus reducing waterproof performance.
In addition, the conventional waterproof sound-transmitting sheet is designed based on a water pressure of about 1 atm, such that when a water pressure of about 5 atm required recently is applied thereto continuously, the waterproof layer is lost in elasticity and thereby is not restored in the state of being stretched toward the protective layer. Accordingly, there is a problem in that in the conventional waterproof sound-transmitting sheet, sound loss and noise due to the collision between the protective layer moved by the sound pressure of a speaker or a microphone and the stretched waterproof layer occur, thus reducing sound transmission performance.
In addition, there is a problem in that the conventional waterproof sound-transmitting sheet is formed with the protective layer to be moved by the sound pressure, such that when the sound pressure of a speaker or a microphone is generated while the water pressure is applied thereto, the waterproof layer is broken by the collision between the waterproof layer and the protective layer, thus reducing waterproof performance, or sound loss and noise occur, thus reducing sound transmission performance.
In addition, there is a problem in that the conventional waterproof sound-transmitting sheet is adhered to a portable terminal through a thin film type adhesive layer, such that when a water pressure of about 5 atm is applied thereto, the waterproof layer is stretched and thereby the adhesive layer is separated from the portable terminal, thus reducing waterproof performance.